This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Lower body negative pressure (LBNP) has been used to simulate loss of central blood volume (e.g., hemorrhage) in conscious, healthy humans. The application of negative pressure to the lower body results in a redistribution of blood away from the upper body (head and heart) to the lower extremities and abdomen, stimulating the same physiological responses as during the initial stages of actual hemorrhage. While LBNP has been used as a model of hemorrhage, the exact equivalence between levels of LBNP and actual blood loss has not been determined. Thus, the purpose of the proposed study is to correlate the physiological responses to LBNP with responses to actual hemorrhage in baboons. The aims of this study are to test the feasibility of using LBNP as a model of hypovolemia in baboons, and to compare cardiovascular and hormonal responses during LBNP and actual hemorrhage.